Electrorheological fluids are compositions that generally include dielectric particles suspended in a dielectric base fluid, and that show a change in viscosity when in the presence of an electric field. Since the dielectric constant is greater than that of the base fluid, these particles are polarized in the presence of an external electric field. Upon polarization in the electrical field, the particles interact by aligning and orienting to form chain-like and/or lattice-like structures within the fluid. In turn, the aligned particles cause an increase in the effective viscosity of the bulk fluid. Removal of the electric field causes the particles to de-orient and to adopt an amorphous configuration, and hence, viscosity in turn decreases.
Typically, such electrorheological fluids include polarizable materials with a low conductivity and a high dielectric constant, such as low molecular weight phenolic/phenolate oligomers, salts of (meth)acrylate oligomers and polymers, and other such materials, suspended in a dielectric fluid such as a silicone or mineral oil. However, there remains a need for electrorheological fluids with improved properties such as a greater range of effective viscosity for a given electrical field strength and loading of the polarizable dielectric material, and a faster response time as well as high temperature performance.